| what is cell theory? | cell theory is that the cell is the structural unit of life that contains metabolic and genetic elements. cells can only arise by division of a preexisting cell. Modern cell theory is that energy flow occurs in cell, heredity information is passed from cell to cell and that all cell have the same basic chemical composition. |
| what are the two major cell types and what makes them different | Prokaryotes have circular DNA free in the cytoplasm, Eukaryotes have a 'true nucleus' linear DNA molecules held in a membrane bound nucleus, contain subcellular organelles to compartmentalise |
| subdivisions of prokaryotes? | Bacteria and eubacteria |
| where is dna located in prokaryotic cells, and how its structured | Nucleoid - not membrane bound, formed into a single loop and does not have introns, genes are grouped into operons |
| describe the plasmid in a prokaryote | small loops of non essential DNA and is smaller than genomic DNA. passes vertically during cell division or horizontally by bacterial conjugation. natural plasmids may carry antibiotic resistant genes. easil manipulated in vitro. |
| describe the difference between vertical and horizontal transmission of plasmid | vertical transmission is when a bacteria goes through binary fission (asexual reproduction), horizontal transmission involves conjugation. |
| what is conjugation? | once replication of the plasmid is completed a donor will produce a pilus which makes contact with the recipient bacterium. pore in the membrane if formed to create a continuous conjugation tube. replic plasmid becomes linear and travels to the recipient where it becomes circular. |
| Ribosomes in prokaryotes | free in cytoplasm (not attached to membrane), composed of protein and rRNA and function to translate mRNA to protein, sedimentation 70s. |
| Storage granules in prokaryotes | store of carbon, either store glycogen or poly-ß-hydroxybutyrate but not both. Glycogen granules dispersed through cytoplasm visible when stained, poly-ß-hydroxybutyrate stains with the fat stain Sudan black |
| what are mesosomes? | aggregates of tubular membrane structures, derived directly from plasma membrane |
| what are the internal membranes in prokaryotes | lamellae, vescles or tubules, appearance in EM depends on bacteria type |
| what are bacterial microcompartments? | protein shells filled with enzymes for key activities,carboxysomes help autotrophic prokaryotes fix carbon via calvin cycle, pdu are involved in propanediol utilisation |
| plasma membrane in prokaryotes | phospholipid bilayer embedded with proteins, do not have cholesterol which are replaced by hopanoids,stabalising membrane |
| plasma membrane function | contains cytoplasm and regulates movement of materials, site of cell wall synthesis, no mitochondria enzymes for energy gen need to be organised within plasma membrane |
| outer membrane function | gram neg, protects invading bacteria from host defence, essential nutrients pass via porins |
| function of bacterial cell wall in prokaryotes | resists internal osmotic pressure, prevents bursting in hypotonic media |
| what is in the cell wall | peptidoglycan, strength is due to cross linking of peptide chains, prevents sugar units of polymer sliding over. |
| capsule in prokaryote | layer of polysaccharide and glycoprotein surrounding the bacteria |
| what is the periplasm | the space between peptidoglycan layer and the plasma membrane, filled with loose peptidoglycan network and enzymes for nutrient acquisition. |
| flagellum in prokaryotes | composed of flagellin low amounts of sulphur containing aromatic amino acids and high levels of aspartic and glutamic acid |
| what colour do gram negative and gram positive bacteria | gram positive bacteria are purple, gram negative are pink what colour do gram negative and gram positive bacteria |
| what is the structure of peptidoglycan | homogeneous |
| teichoic acid | glycerol ribitol or manitol polymers in gram positive cell walls |
| describe the gram negative cell wall | thin layer of peptidoglycan,overlaid by a lipid layer similar to plasma membrane |
| microbial diversity | considers the vast array of microorganisms |
| what are acidophiles | bacteria that can grow at a pH of 3 or below, they need to maintain a net outflow of protons to maintain the internal pH |
| what can acidophiles be used for commercially | can be used to leach metals from low grade ores |
| what are alkalophiles | bacteria that are inhibited by pH 8-9 or above, must maintain a net inflow of protons to preserve internal pH, example is Vibrio cholerae |
| what are the three groups of oxygen requirements for bacteria | aerobes - depend on molecular oxygen
facultative anaerobes - use oxygen if available
anaerobes - cannot use oxygen |
| Aerobic bacteria | found in terrestrial and aquatic habitats, don't grow in static liquid culture, require shaking |
| facultative anaerobes | commonly used andmedically significant E.coli, require fermentable sugars |
| Anaerobic bacteria | some killed by oxygen (obligate),others are tolerant, depends on superoxide dismutase |
| what is the importance of superoxide dismutase | destroys toxic superoxide radicals dormed during oxidation, converts superoxide radical to hydrogen peroxide and oxygen |
| Temperature - Psychrophiles | grow well at 0 optimum near 15, found in arctic, membranes are high in unsaturated fatty acids |
| Psychotrophs | grow at 0 but optimum is between 20-30, present in soil, cause of food spoilage |
| mesophiles | growth optimum around 20-40, majority are mesophiles, includes bacteria that live in association with or cause disease in animals |
| Thermophiles | optimum about 55-65, grow in compost, enzymes and nucleic acids are heat stable, membrane lipids more saturated than mesophiles |
| Hyperthermophiles | grow above 90, optimum between 80-113, includes species which grow in hot areas of ocean |
| Black smoker' bacteria | grow in sulphide chimneys, grow at 113 ' |
| Halophiles | can tolerate high salt levels can colonise saline lakes, cell wall may be damaged from low salt concentrations |
| are eukaryotes unicellular or multicellular | Eukaryotes can be both unicellular and multicellular |
| DNA molecules in Eukaryotes | have linear DNA molecules packaged as chromosomes enclosed in nucleus, have membrane bound organelles |
| unicellular eukaryotes | most complex eukaryotes, perform all functions, unicellular when food available, when food is scarce they aggregate and specialise to form primitive multicellular organism |
| what are Eukarytotic cell membranes composed of | phospholipids and protein, spontaneously assemble to form closed bilayers |
| Eukarytoic cell membranes: two faces | The two faces of the cell membrane are asymmetric in terms of lipid and protein composition Cytosolic face is the inner part, exoplasmic face is the outer part. |
| Functions of plasma membranes | regulation of transport
balance of chemical conditions
chemical reaction site
detects signals
interacts with other cells/extracellular (multicellular) |
| Name the organelles of the eukaryotic cell | Nucleus, ER, golgi complex, mitochondria, lysosomes (ac), peroxisomes, cytosol, cytoskeleton |
| Nucleus | contents are in contact with cytoplasm via nuclear pores which pass through both membranes
Large dense region= Nucleolus, rich in protein and RNA |
| What does the nucleus separate | separates DNA from the cytosol; transcription from translation |
| ER- two types and what they do | Extensive membrane structure forming interconnected sacs and tubules
Rough ER= ribosomes attached to surface, plays role in synthesis of membrane-bound and secreted proteins
Smooth ER = no ribosomes, plays role in producing lipids |
| ER | lipid synthesis, membrane protein synthesis, Ca 2+ ion storage, detoxification
Key features:
interconnected closed membrane tubules and vesicles |
| Ribosomes | multi-subunit structures, 50% protein, 50% ribosomal RNA
rRNA key to structure and function of ribosomes
synthesis of proteins
40s and 60s subunit= 80s |
| Mitochondria | Contains DNA and ribosomes, can direct production of some of own proteins
self replicating = binary fission site of ATP production, aerobic metabolism, important role in apoptosis
Key features:
outer membrane
intermembrane space
inner membrane
matrix |
| what is apoptosis? | programmed cell death |
| Mitochondrial DNA | Genes exhibit cytoplasmic inheritance and encode rRNAs, tRNAs, mitochondrial proteins
size and coding capacity of mtDNA varies
products of mitochondrial genes are not exported
mutations cause genetic diseases, leigh syndrome, optic neuropathy |
| Golgi complex | stack of flattened membranous sacs vary in number
sacs form from parts of rough ER which break off and fuse
Inner face is close to the nucleus
ensures that vesicles budding off outer face can fuse with plasma membrane
packages lysosomal proteins and proteins to be secreted from cell |
| Lysosomes | single membrane-bound organelles containing hydrolytic = degrade materials taken up by endocytosis and cell debris
degrade damaged newly synthesised proteins |
| peroxisomes | single membrane-bound organelles
contain catalase and urate ocidase = breaks down very long chain fatty acids via beta oxidation
oxidation of toxins |
| cytosol | enclosed by the plasma membrane
not static contents continuously moving
key features:
cytoskeleton
polyribosomes
metabolic enzymes |
| cytoskeleton | lattice like array of filaments and fine tubules
involved in cell movement, division, maintenance, trafficking organelles
3 major components:
microfilaments = actin
microtubules
intermediate filaments |
| microfilaments | F-actin filaments are double helices of polymerised G-actin subunits
fibres expand and contract by further polymerisation and depolymerisation, ATP dependent
Interact with other filaments and 'motor' to create movement,contraction can cause shape change |
| actin and myosin in Eukaryotic cells | Actin microfilaments work with myosin in muscle fibres
myosin filaments walk along the tethered actin, pulling the filaments towards the centre to cause muscle contraction |
| microtubules | Microtubules are polymers of tubulin that form part of the cytoskeleton
tubes of tubulin: grow by polymerisation from specific microtubule organising centres
microtubules can form trackways in cellsalong which motor proteins (kinesins) drag vescles, organelles.
Play a fundamental role in partitioning of chromatids in cell divisions |
| microtubules role in cell division | partitioning of chromatids
chromatids are one of two strands of a newly copied chromatid, two joined together at centrimere they are called sister chromatids and are genetically identical |
| intermediate filaments | different types that differ in composition and function, may have role in maintaining cell shape, tissue integrity |
| what are the specialised features of plant cells? | chloraplasts, vacuoles and specialised peroxisomes
plant cells have a rigid cell wall
can communicate with eachother |
| vacuoles | make up 80% of plant cell
store water, ions, nutrients, degrade macromolecules
inflow of water by osmosis causes vacuole expansion and maintenance of turgor pressure
expansion of vacuole involved in cell elongation |
| Chloraplasts | double membrane bound, contain their own DNA
Thylakoid membranes, fused into stacks in places, contains chlorophyll
photosynthetic plant cells, contain chloraphyll to absorb light and generate NADPH and ATP |
| specialised peroxisomes | found in leaves involved in photorespiration (oxygen to carbon dioxide)
Glyoxysomes found in germinating seeds, carry out glyoxylate cycle to convert fatty acids into sugars |
| plant cell wall | rigid cell wall comprised mainly of cellulose cross linked by hemicellulose, pectin, and lignin |
| Plasmodesmata | directly connect the cytosol of adjacent cells in higher plants |
| name the different tissues that cells that are organised into | epithelia, nervous tissue, connective tissue, muscle, blood |
| what is the process of cells going to tissues | Differentation |
| why are the layers of the early embryo important? | They give rise to the cell types, goes from xygote to blastocyst and then gastrula
Germ cells = sperm or egg
endoderm (internal) layer = lung alveoli, thyroid, pancreatic cell
Mesoderm (middle) layer = cardiac muscle, skeletal muscle, tubule cell of kidney, RBC, smooth muscle.
Ectoderm (External layer) = epidermis skin cells, neuron, pigmant cell. |
| cells produced at 50-cell stage? | cells that are produced at the 50- cell stage are called Embryonic stem cells, these cells are totipotent except foetal membranes) |
| what is totipotent? | ability of a single cell to divide and produce all of the differentiated cells in an organism. |
| what is a pluripotent stem cell? | A pluripotent stem cells give rise to cells to a particular tissue |
| what is a monopotent stem cells | monopotent stem cells can produce only one cell type |
| can adult cells be reprogrammed? | Adult cells can be reprogrammed by manipulating the expression of key regulatory genes to produced induced PS cells, derived from blood or skin cells. |
| differentiated cells | differentiated cells express different subsets of genes: transcribed genes (transcriptome), and translated proteins (proteome). |
| Mechanism and Differentiation | tissue specific gene expression is primarily regulated at the level of transcription, fine tuning at post-transcriptional and post-translation levels also occur.
Signals received by the cell activate transcription factors to turn on certain genes.
Inactive genes are characterised by methylation at CG doublets in their promoters |
| what are the four major classes of cell surface receptors | G-protein couples receptors
Tyrosine kinase-linked receptors
Ion channels receptors
receptors with intrinsic enzymatic activity
Singles generated at the plasma membrane are transduced to the nucleus via a complex series of secondary events |
| Name the secondary events in transducing signals from the plasma membrane | binding of the second messengers to receptors and phosphylation |
| Apoptosis role | has roles in embryogenesis, tissue homeostasis, damage limitation, control and functioning of immune system.
Evolutionarily conserved and genetically controlled |
| what are the Two main gene families involved in apoptosis | Bcl-2 family (regulation)
Caspase family (execution)
Many accessory proteins - death domain proteins |
| characteristics of apoptosis | Mild convolution, chromatin compaction, margination condensation of cytoplasm
Breakup of nuclear envelope, nuclear fragmentation, Blebbing cell fragmentation
Phagocytosis |
| Importance of Apoptosis | Too little apoptosis can lead to cancer, autoimmune diseases and prolonged viral infection
Too much apoptosis leads to neurodegenerative diseases, autoimmune, tissue damage through trauma, progression of AIDS. |
| how does apoptosis become unregulated? | Genes controlling it become damaged or aberrantly expressed, inappropriate triggering of apoptosis, the interference by exogenous genes |
| name cell types: Epithelia | Epithelial cells - from sheets that cover the inner and outer of the bodies surfaces
Absorptive cells - have microvilli to increase their surface area
ciliated cells - have cilia that beat to move substances over the sheet
Secretory cells - secrete substances out onto the sheet |
| What are the main types of intestinal cells | Absorptive cells outnumbers others 10:1
Goblet cells: secrete mucous
Paneth cells: secrete growth factors and antibacterial substances
Enteroendocrine cells: secrete peptide hormones and serotonin into gut wall |
| Name 3 Neuron cell types | Neurons are specialised for communication, the axon conducts electric signals away from the cell body
multipolar interneurons
motor neurons
sensory neurons |
| Cell types: rod cells, what are they? | Rod cells are specialised sensory cells in the retina, layers of disks contain light sensitive pigmant = rhodopsin
Light evokes an electrical signal that is transmitted to the brain |
| Cell type: Erythrocytes, what are they? | highly specialised, carry oxygen, protein component is haemoglobin
loss of nuclei and internal membrane, cant replicate |
| Connective tissue, name some different connect tissues that arise from fibroblasts | fills spaces between epithelial sheets and tubes
Bone cell - osteoblasts/osteocytes
Fat cells - adipocyte
smooth muscle cell
Cartilage cell - chondrocyte |
| what does fibroblast differentiation depend on | Depends on the etracellular matrix
YAP and TAZ are transcription regulators that move to the nucleus in response to tension developed in the actin-myosin bundles in the cytoplasm |
| What does the transcription regulators YAP and TAZ stand for | YAP = yes associated protein
TAZ = transcriptional coactivator with PDZ-binding motif |
| what are the different types of muscle cells | Cardiac muscle - in the wall of heart, adjacent cells connected by electrical conducting junctions to ensure synchronous contraction
Skeletal muscle - striated muscle fibres, made from large multinucleated cells. control voluntary movement
Smooth muscle - thin elongated cells non striated, control involuntary movement |
| what are the requirements for a multicellular organism | Interactions:
Cell adhesion molecules
tight junctions, gap junctions, adherens junctions
Desomosomes
Interactions between cells and their surroundings:
Hemidesmosomes and focal adhesions
basal lamina
Extracellular matrix - integrity of tissues |
| major classes of cell adhesion molecules | Homophilic interactions:
Cadherins (E-cadherin)
Ig-superfamily
Heterophilic interactions:
Integrins (alpha v beta 3)
Selectins (P-selectin) |
| tight junctions? | Sometimes cells need to form an impermeable barrier, tight junctions seal gaps between cells, the membranes are firmly pressed together and prevent leakage. |
| tight junction proteins | The role of tight junctions are too seal off body cavities and restrict diffusion of membrane components.
Proteins:
Claudins: important in structure and sealing
Occuludins: determins junction permeability |
| What are gap junctions? | Series of pores connecting adjoining cells and forming a cytoplasmic bridge,also provides a chemical and electrical coupling between adjacent cells.
Permit the movement ions and small molecules of MW less than 1200 between cells |
| Gap junction functions? | Allow co-ordination of activities in a sheet of cells, example of this is beating cilia, allows rapid transmission of nerve impulses, these impulses can pass through cells, rather than having to jump across synapses.
Gap junction are important for intercellular signalling. |
| Aherens junctions? | connect the contractile bundles of actin and myosin filaments that run parallel to the plasma membrane, allows contraction of the epithelial tubes.
The loss of cadherin ( protein involved in interaction) is associated with metastasis in cancer |
| Components of adherens junctions | External homotypic interactions between E-cadherins and interactions between catenins and actin microfilaments |
| What are desmosomes? | button like contact points that rivet cells together, connect the intermediate filament networks of adjacent cells
Desmosomes anchor the cells cytoskeleton to the PM and connect the cytoskeleton to surrounding cells giving strength |
| desmosomes and hemidesmosomes | within the cell, intermediate filaments connect with adjacent desmosomes and hemidesmosomes to produce a cage-like skeleton.
Hemidesmosomes anchor the cell to the basal lamina |
| Integrin-containing junctions | Integrin-containing junctions connect cells to the substratum
Laminin and fibronectin are multi-adhesive proteins that bind to components of the extracellular matrix
Multi-adhesive proteins that bind to multiple components of the extracellular matrix and cells |
| basal lamina? | network of proteins and proteoglyans connected to the plasma membrane
Specialised region of extracellular matrix that provides a solid substratum to anchor epithelial cells, forms a barrier between epithelial sheets and connective tissue.
different forms in different tissue |
| what is the ECM? | ECM is a fibrous network of proteins and polysaccharides that fills the spaces between cells. hold cells and tissues together. role in embryogenesis, wound healing and cell migration. Proteoglycans - protein core linked to glycosamineoglycns form a hydrated gel-like substance into which fibres are embedded
Fibrous protein - structural, adhesive or elastic |
| What does GAGs stand for? | glycosaminoglycans |
| GAGs, what do they do? | They occupy much of the extracellular space
extremely hydrophilic, adopting extended conformation to form hydrate gels |
| what are Elastic fibres? | allow tissues to stretch and recoil, some tissues need both strength and elasticity (blood vessels)
Composed of elastin deposited on glycoprotein-based microfibrils with crosslinks
is interwoven with collagens to limit extent of stretching |
| What are the functions of the plasma membrane? | Interface between a cell and its environment
Barrier: regulates transportation
Attachment point for intracellular cytoskeleton |
| what is diffusion? | the net movement of molecules from a region of a high concentration to a region of lower concentration
occurs down a concentration gradient, move down until they are equal |
| equation of rate of diffusion? | (surface area x difference in conc)/thickness of surface |
| what does rate of diffusion depend on? | surface area across within diffusion occurs - larger the SA the faster the diffusion
Thickness of surface - thinner the surface the faster the diffusion
Difference in con - the larger the difference in conc gradient faster the diffusion
Hydrophobicity of a substance, measured by its partition coefficient, K - the higher a substances partition coefficient, the more lipid-soluble it is |
| what is osmosis? | the process by which molecules of a solvent tend to pass through a semipermeable membrane from a low conc to a high conc solution |
| What are the osmotic effects? | Hypertonic - solute is more concentrated causing cells to shrink
Isotonic - equal salt and water conc, normal cell shape
Hypotonic - lower conc of solute in the cells, causing cells to swell and burst |
| Differentiate between the different types of transport? | Simple diffusion - no transporter molecule is used and transport is according to the concentration gradient
Passive transport - transporter molecule is needed but no energy is required as the transport is down the conc gradient,can use channels and occurs spontaneously.
Active transport - transporter requires energy to move a substance against the conc gradient, transporters in active transport are called pumps |
| Membrane permeability? | rate of diffusion depends on the permeability coefficient (P) of the membrane to transported solute and its conc on either side of membrane |
| what does the permeability coefficient depend on? | K: partition coefficient (hydrophobicity of solute),
D: diffusion coefficient of solute (rate of diffusion across the membrane based on molecular weight / size of solute)
Δx: width of the membrane (Δx) |
| Facilitated transport? | If the measured permeability of a solute is higher than expected = facilitated transport
Channels form a hydrophilic tube or passageway across the membrane through which multiple water molecules or ions move simultaneously , single file at a very rapid rate. Some channels are open much of a time whereas others require activation upon specific signals. These channels are referred to as gated channels. – very selective. |
| what are aquaporins? | form a pore across the bilayer, its tetramer, selective passage of water molecules
shaped like an hourglass. |
| Name some Ion channels used in facilitated diffusion | Gated channels - Ligand, voltage, mechanically |
| Voltage-gated channels? | voltage-gated channels respond to changes in the membrane potential. resting varies between -20mV and -200mV interior more negative than exterior. |
| ligand gated channels? | respond to the binding of a ligand, could bind extracellulary (neurotransmitter) or intracellulary (ion or nucleotide) |
| Mechanically gated? | channels respond to mechanical stress, those channels may have cytoplasmic extensions that interact directly with the cytoskeleton. |
| What is the potassium channel | Transfers K+ out of the cell, facilitated diffusion,complex of 4 subunits with a Tepee arrangement main helices tilted at 25 degrees, each subunit contributes an inner pore lining helix and an outer structural helix. |
| Potassium channel | The central pore is filled with water which allows potassium ions to remain hydrate, Three potassium binding sites each provided from main chain C=O groups.
Selectivity filter = Formed from conserved sequence residues 75-79, 75-78 bind potassium in two positions, third ion in cavity.
Peptide bond carbonyl groups provide rings of O atoms
Electrostatic repulsion ensures high movement throughout |
| what is selectivity due to in the K+ channel | selectivity of K+ is due to a hydration compensation mechanism, rings of oxygen are placed to compensate for loss of K+ hydration shell but not Na+ hydration shell (Na+ is too small to fit into the ring)
controlled by a gating mechanism, minor structural changes that serve to obstruct the entrance to the pore. |
| what are ionophores? | Microbial low molecular weight products that make the membrane permeable to ions
Gramicidin A
15 residue protein from Bacilus brevis
Forms a cation specific pore, requires to molecules
Causes equal distribution of K+ and Na+ between environment and cell interior cell death
Topical antibiotic |
| Transporters? | Transport can be passive (uniport) or active (symport and antiport)
Slower rate than channels
Uniporters transport molecules down their conc gradient
symporters and antiporters move one against the conc gradient |
| what are symport and antiports | Symport transports two different substances in the same direction
Antiport transports two different substances in opposite directions |
| Glucose transporter? | uniporter -selective for glucose, 12 transmembrane a-helices
Facilitated diffusion - requires conc gradient
conformational changes allow glucose to move through the protein not flipping |
| what are the kinetics of passive transport? | Simple diffusion = rate is directly proportional to conc of solute, higher the conc of the solute the higher the rat of diffusion
Transporter-mediated diffusion = Transporter proteins varying affinity for their solute, have varying maximum rate, when transporter is saturate they will reach maximum rate
Analogous to a biochemical enzymatic reaction |
| what are coupled transporters? | they couple the transport of one solute down their conc gradient, with the transport of one solute against their conc gradient |
| what are light driven pumps? | found in bacteria and archaea and couple transport of a solute (H+) from energy from light (bacteriorhodopsin) |
| atp driven pumps? | Use energy released by hydrolysis of ATP to transport ions and molecules against their concentration gradient
ATP binding site in the cytosolic side
Four main classes
P-class: require the catalytic subunits to be phosphorylated as part of transport cycle
V-class: not phosphorylated, will transport protons
F-class: not phosphorylated, use the conc gradient of protons to synthesis ATP
ABC transporters: transfer small molecules and are also found in bacteria |
| what is sarcoplasmic reticulum? | specialised type of endoplasmic reticulum that serves as the intracellular store of Ca2+. |
| P-type ATPases? | sarcoplasmic reticulum Ca2+ pump:
- low Ca2+ cpncentration, high within SR
- Ca2+ is transported against its conc gradient
- Antiporter
Na+/K+ ATPase
- high conc of Na+ extracellularly, high conc of K+ intracellularly, maintains the conc gradient, Antiport |
| What type of pump is the calcium pump? | its a P-type ATPase, contains multiple transmembrane helices coupled to three domain in the cytosol:
The nucleotide binding domain (N), phosphorylation domain (P), and the activator domain (A)
N domain = contains the ATP binding site
P domain = contains the aspartate that is phosphorylated
A domain = contains phosphatase activity that dephosphorylates the phosphorylated P domain |
| What is the first step in Ca2+ transport? | When the ATP pump is in the ATP bound state, the pump is open to the cytosol allowing two calcium ion to bind in a pocket formed by the transmembrane helices. |
| Second step in Ca2+ transport? | when calcium is bound, the pump closes, and ATP is hydrolysed. This results in the transfer of a phosphate group to a conserved aspartate (Aspartate 351) in the P-domain.
In this state, the calcium ions are trapped between the helices within the membrane. |
| Third step in Ca2+ transport? | The shift to the E2 state causes ion binding sites to 'evert' so that the ions can dissociate into the luminal side of the membrane.
ADP id exchanged for a fresh ATP resulting in the pump to open to the lumen of the SR releasing the calcium ions.
binding of 2 H+ from the SR and the closing of the pump and the dephosphorylation of the P-domain |
| Step four in the Ca2+ transport? | In the E2 -P state, the enzyme has low affinity for the Ca2+ ions, so they are released |
| Step five in the Ca2+ transport? | With release of the Ca2+, the phosphoaspartate residue is hydrolyzed, and the phosphate group is released. |
| Step six in the Ca2+ transport? | Does not have a covalently attached phosphate group and therefore not stable so verts back to E1 form.
Calcium ATPases play an important role in cell signalling as well as Ca2+ can act as a signalling molecule. Maintaining low concentration of CA2+ inside the cell also allows for the signal to be quickly transmitted. |
| P-type ATPases Na+/K+ | Insert 2 potassium ions and remove 3 sodium ions
Na+ gradient drives transport of nutrients as with glucose.
Regulates cytosolic pH
More than 30% of an animal cells energy is used to fuel this pump – nerve cells and cells involved in transport this could increase up to 70%.
Electrogenic - drives a net electric current across the membrane.
As with the calcium pump an aspartate is phosphorylated |
| Pumping Na+? | Pumping Na+ against its conc gradient requires energy, provided by cleaving ATP, the ATP transfers a phosphate group to the pump in a high energy linkage.
Phosphorylation causes a dramatic change in the pumps conformation, sodium ions become exposed and released outside of the cell.
This also exposes binding sites for potassium ions in the pump.
There are two potassium-binding sites, binding of the potassium ions triggers release of the phosphate group and return the pump to its normal conformation |
| Summery of P-type ATPase | Creates a sodium and potassium concentration gradient
Pump is electrogenic
Per 1 ATP hydrolysed, 3 Na+ ejected, 2 K+ taken up, 1 positive charge ejected
ts action creates an electrical potential difference across the plasma membrane
Antiporter, up-hill glucose transport, net carbohydrate and protein absorption, cell volume, resting potential |
| V-type ATPases? | found in Eukaryotes
13 subunits
stands for vacuolar transporters
Transports protons across internal membranes
They generate the low pH of plant vacuoles and of lysosomes and other acidic vesicles in animal cells by pumping protons from the cytoplasm to the lumen of the organelle. |
| F-type ATPases? | Found in bacterial plasma membranes, mitochondria and chloroplasts
Reverse proton pumps (ATP synthase)
Use the energy from proton gradient to synthesise ATP |
| ABC (ATP binding cassettes) transport protein? | When ATP is not bound the binding site is in the cytosol, when atp is bound the binding site is open at the ectracellular side.
78 ABC transporters in E.coli – mono and polysaccharides, peptides, lipids, drugs and even proteins. |
| Multidrug resistance protein (MDR) | ABC transporter highly expressed in many human cancer cells
Pump drugs out of the cell
Makes cells resistant to various cytotoxic drugs used in cancer chemotherapy |
| what is so special about proteins, DNA and RNA? | all molecules conform to physical and chemical laws
nucleic acids and the protein they encode display properties appearing to transcend these laws (life)
Proteins act s cellular components with very precise structures, defined by sequence information
Many proteins are highly specific catalysts allow large number of chemical reactions in the cell without interfering with each other. |
| what is the importance of protein structure? | The importance of the protein structure is that anything that needs to be bind is bound in the right position to give the desired effect. EXAMPLE: for lysozyme, binding to the polysaccharide substrate is very specific, each atom making contact is in precisely the right position for binding and catalysis.
Lysozyme is part of the innate immune system. The specificity of reaction is determined by the precise array of charges and hydrophobic elements in the protein ie. by exact structure of each protein, this structure is determined by the sequence of AA in the polypeptide chain, which is in turn determined by the DNA bases encoding this gene. |
| The central dogma molecular biology | - info in DNA conserved with high fidelity by DNA replication
- during gene expression, info is passed from DNA to mRNA
- The info then passes from mRNA to protein by translation (translating the info from a nucleotide language to an amino acid language) |
| what are genomes? | The genomes is the total of all genes |
| What are genes made of? | genes are made from DNA, however virus genes are made of DNA or RNA
The role of DNA is to encode proteins |
| Why are genes switched on and off in different tissues? | some are always on, known as housekeeping genes (genes encoding enzymes for glucose metabolism or protein synthesis)
Other genes are only switched on in cells where needed eg. muscle myosin genes, B-lymphocytes in immune system. |
| Are genes lost when they are not used in the cell? | genes are not lost when not in use. If the nucleus from a differentiated cell is transplanted to an empty egg a complete animal can be produced and therefore shows that genes are not lost. |
| Problems with human cloning? | Technical problems, many ethical issues to be addressed, potential of defective babies.
more realistically used to produce stem cells for therapy eg. neurodegenerative diseases and diabetes |
| What is the difference between reproductive and therapeutic nuclear transplantation? | Therapeutic cloning is the technique that is used to develop specialised cells for stem cell therapy whereas reproductive cloning is using the nucleus from one 'being' and an egg cell from another and producing an exact living clone. |
| Explain how DNA was established as the molecule that carries inherited info? | - In the 1920’s Fred Griffith reported that a “heat-killed extract” from pathogenic bacteria could convert harmless ones to pathogenic ones.
- Purified DNA was shown to produce the same effect. Genetic properties can be transferred from one bacterial strain to another by extracting DNA from the first strain and adding to another strain (Transformation) |
